Chain oscillator in a multiplex system



April 3, 1956 H. GOLDBERG 2,740,893

CHAIN OSCILLATOR IN A MULTIPLEX SYSTEM Filed Dec. 31, 1947 2Sheets-SImeet l v PULSE INTERVAL CHANNEL No. 1 GENERATOR CONVERTER I 11-iO A CHANNEL PULSE INTERVAL I No. 2 GENERATOR CONVERTER F PULSE INTERVALI I GENERATOR CONVERTER I T v l 14 ll 1o PULSE l TERVA SUMMER N LGENERATOR CONVERTER CHANNEL No. "N"

,Ia TRANSMITTING DEVICE I 1H". 1

HAROLD GOLDBERG I I I I April 3, 1956 I H. GOLDBERG 2,740,393

CHAIN OSCILLATOR IN A MULTIPLEX SYSTEM Filed Dec. 51, 194'? 2Sheets-Sheet 2 PULSE TRAIN TO F j TRANSMITTING DEVICE l I I l J CHANNELCHANNEL T NO. "N" J HAROLD GOLDBERG 2,7403893 CHAINOSCILLATGR INA.mutrtrrznx;

Harold" Goldberg; Towson; MHZ, assighbr'to Benifix Avie:

tioniCorpo'r-atiomTowson;Min; amorporafibn of Delaware" ApplicationDecember-.31, 1947,,SerialNo. were. zzcnima. (cmso ssyThisinvefitionrrelates to a system oftiririe division m'uL fipleitiiigusin pulse niodnnribn" techniques Previously known timedivisionmultiplex systems: operat'ein the'following manners If'richannels are to be utilizedan'd'if fis the highest frequency tobetransrnitted th'ereover, .abasic repetition rate ineitcesspfZfiisestab} lished by a stable oscillator. Pulses dent/e23 from this sourceat the basic repetition rate establish the. reference for.the.periodictransmission of the. information in each of..th'e:nchannels. In other words, following;the transmission. ofthis' basic orsynchronizing pulse,- phr se responding .to the information in each ofthe n. channels in. sequence. are. transmitted beforev the next basic,or synchronizing,pulse. I k

[The channel pulses. transmit. information asfollows.

The time between synchronizing pulses. T, when; isj the' reciprocal ofthebasic rep etitionrate' R, is divided into it equal intervals.Starting withthe first, these" are-. nu-

merically a ss igned tosthe-n channels, 1. to. n. these. intervals. is achannel time space, during which corresponding channel information istransmitte 7 means of thepositionof a pulse: therein. (The ihf orma:tion conveyed-bythe channelis actually defined by; the interval betweenthe synchronizing pulse. and the channel pulse.) Thus; thechannelinforniation. for. cha

nnels' 1 to rr istransrnitted sequentially, followingka synchronizingpulseand this seq uence isrpeated at the ratev t In the previously knownsystems thechannel-pulseTis sentat the. center of. the channel intervalthe channel inpubi's: zero. Positive and negative channel input.plitudesare linearly translate'dinto, delays and advances relative-tothe center of thechannel interval, ,or vice verse,

The'operatio'n of systems oif the fore'g oi r'jn g. typeis suhiect toncertain; disadvantages. I For. example, t chronizing; pulse. carries no;information. period T, n plus. 1 pulses'are required t conyey int tion.overn channels:- While this is of little inip rt ce for large valuesofn, it becomesa matter.of-co n srdr l e importance when n is small.Furthermore, if the synchronizingwpn-lse is characterized by;agreaterpulse length than that of the. channel pulses, for values of nless than 10 a considerable portion" of the" average transmittedpoweris' being sent merelyasa reference, without inhe'rent lycarryingany-information. v

Guard intervals,-which represent' al'oss in transmission timeutilization, must be established between channel intervals. The use ofthis lost time would provide a greater signal to noise ratio for thesame number of channels or a greater number of channels for the samesignal to noise ratio.

Clippers or compressors must be employed to prevent channel pulses fromgetting out of their assigned intervals, since overmodulation results invery objectionable distortion. The clippers will in themselves, ofcourse, cause distortion in the ofiending channel.

It is an object of the present invention to provide a time divisionmultiplex system which is free from the above defects.

2,740,893 7 P-atented Apr.- 3, 1956 ICC 2 Itis a f ugther objectof theinvention to provide a mul tipl'ex sy'sftemin. whichthe guard intervalsbetween chan nels. may be greatly reduced. 7 is another object of theinvention toprovide a multiplex system inwhich overmodulation results invery lit :le ihstortion which is easily maintained at. aharmless eveItis still another objectto provide a multiplex system which thesynchronizing pulse may carry channel in'- ma i n-..

It is e still iurtlier object to provide a; multiplex system in which itis-impossible to overmodulate-in the sensethat channelpulses will-occurin other than normal sequence.

The above and other objects are realized by'a-;-sy stem-in whiclr eachchannelinterval, the magnitude of which is a function ofl thfeinformation itcarriea-is" measured, not fi om the synchronizing pulse,but from theterminatiomof thepulse of the preceding channel. The channelinteryal has a reference-magnitude for a condition of nomodulation, Itvariesin magnitude about-this reference. mag? nitude as a function ofthe modulation applied. The nth channel is terminated by'the synchpulse, the trailing edge channelas indicated the converter of channel itbeing connected .to the converter of channel 1.

To; each converter is' also connectedarespective pulse generatorindicated by the blocks 11: The outputs of all the pulsegenerators areapplied -to a summer-IZthe Out put; ofwhic-hoperates atransmittingdevicd13. The methodof transmission is immaterial. Ifcarrier trans= missionisusedthe device 13 is a carrier generator.

Information to be transmitted inany particular chanz nel; is appliedtothe intervalyconverter of thatv channel; Each of; these-convertershasthe property that it may be triggered-'intoa statedifierent from itSre'sting state an'd wilLr-emain in that state for aninterval-determinedby theinformation reaching it from its channel input.When it-returnstoits resting state, ittriggers otf-the'next con verter-10,in-the sequence by means of the'sequential connection l i shown;Whentheconverter'of'the nthchannel returns to its equilibriumstate;-it-triggers otf' the con verter of channel No.1 by wayofthejconnection- 15; In this-way, the/separate. channel intervals aregenerated .:in sequential fashion. The chain acts as a form of oscilla rtor,;the group time beinga function of the information onall ofthechannels, v The return. toequilibrium of any'converter 10 not onlytriggers the following converter but; also triggers the pulse generator1-1; connected," to it, which generator 0p.- eaates once for each itriggen; The; pulse generator=of charmed No. l generates thesynchronizing pulse. The remaining pulse generators are all alike andgenerate identical channel pulses. The synchronizing pulse may bedifferent from the channel pulses in shape, amplitude, width, etc. Ifdesired it may be a multiple pulse with a definite coding.

Fig. 2 shows the transmitter in more detail. Each interval converter 10comprises a flip-flop circuit which is a relaxation oscillator of themultivibrator type having one stable and one unstable condition. Sincethe multivibrator circuits are identical, the description will beconfined to that of the N0. 1 channel.

The multivibirator circuit of this interval converter comprises the twotubes 16 and 17 coupled by a time constant circuit comprising thecondenser 18 and resistor 19. in the equilibrium state of themultivibrator the tube 16 is nouconducting and the tube 17 isconducting. Upon the application to the control grid of the tube 16 ofthe equilibrium voltage output of the nth stage the tube 16 is renderedconducting and the multivibrator goes into its unstable state. Theduration of this state is deter mined by the values of the time constantcircuit.

Modulation of the channel interval is accomplished by the application ofmodulation voltage through a transformer 20 the secondary of which is inseries with the I output from the interval generator of channel No. 1

resistor 19. This voltage varies, in accordance with its magnitude, thetime required for the discharge of condenser 18 to the firing level oftube 17. The output of the multivibrator is taken from the anode of tube16 by conductor 14.

Some means is required for initiating the oscillation and to reestablishit if it ceases. It is necessary that the initiating device trigger onlyone circuit once and then remain quiescent unless the oscillation fails.If this occurs, the device must again trigger the chain a single timeand then remain inoperative as long as oscillation continues.

This is accomplished by a blocking oscillator circuit comprising tube 21having its grid and anode circuits inductively coupled to each other andto the cathode of tube 16. Connected between the grid of this tube andground is a condenser 23 by-passed by a resistor 24. A diode 25 has itsanode connected to the ungrounded end of resistor 24 and its cathodeconnected to the junction point of a condenser 27 and a resistor 26which are connected in series between the output of the followinginterval converter and ground. Additional diodes connected to otherinterval converters may be used if necessary.

When the circuit is first energized, the capacitor 23 is uncharged.Under this condition the blocking oscillator will fire. The pulseproduced initiates the chain oscillation. The firing of the blockingoscillator also results in the negative charging of condenser 23 whichblocks the oscillator until enough charge leaks off through resistor 24to reduce the grid voltage to the firing point. The condenser 23 isconnected, however, to one or more elements of the oscillator chainthrough diodes such as 25. The initiation of an unstable state in achain element to which a diode 25 is connected causes condenser 23 to becharged negatively again. As long as the chain continues to run, and thetime constant RC of components 23, 24 is sufficiently long, the blockingoscillator cannot fire. If the chain stops oscillating, the charge on 23leaks off and the blocking oscillator again operates to start to theoscillation. The time required to reinitiate the oscillation after thecessation of oscillation is a function of the time RC. This time may bemade shorter by using several chain oscillator elements to charge thecondenser 23.

As pointed out above, completion of the transmitter requires thederivation of a train of pulses corresponding to the interval divisiontimes. The pulse generators 11 and the summer 12 which perform thisfunction are shown schematically in Fig. 2. Since the pulse generatorsare identical in make-up, only the one operating upon the I variouspulse generators.

will be described.

Each pulse generator 11 comprises a blocking oscillator having a delaynetwork and generating approximately rectangular pulses. The blockingoscillator comprises a tube 30 having its grid and anode inductivelycoupled as indicated at 31. The grid circuit is provided with a delayline 32 and the output of the respective interval generator is appliedto the grid circuit by way of a cathode follower 33. The pulse lengthdepends upon the time constant of the delay network. One method ofcharacterizing the synchronizing pulse is to make it longer than theothers.

Summation of the pulses to form a pulse train may be accomplished by anumber of methods, the one illustrated here involving a circuit 12comprising a series of induc' tors, inductively coupled to the outputcircuits of the The summed pulses are then transmitted either as videopulses, or by modulating a carrier.

In the foregoing, the embodiment of the invention now preferred has beendisclosed. Many modifications in circuit structure and arrangementfalling within the scope of the invention will, however, be apparent tothose skilled in the art.

What is claimed is:

1. In a pulse time multiplexing system comprising a chain oscillatorcomposed of elements, each of which has a normal stable state and iscapable of being triggered into a temporary unstable state, the returnof each of said elements to its stable state triggering the nextfollowing element into an unstable state; means for reestablishing saidchain oscillation upon its interruption, said means comprising ablocking oscillator having its output coupled to one of said elementswhereby the operation of said blocking oscillator excites said chainoscillator into operation, an energy storage device forming a part ofsaid blocking oscillator and when charged maintaining said blockingoscillator in its blocked condition, means bleeding the charge from saiddevice and means recharging said device from the output of a succeeedingelement of said chain oscillator.

2. The combination comprising a chain oscillator formed of a pluralityof sequentially connected oscillating elements, the oscillation of eachelement triggering the next succeeding element into oscillation, andmeans for reestablishing oscillation in said oscillator uponinterruption thereof, said means comprising a blocking oscillator havingits output coupled to one of said elements whereby operation of saidblocking oscillator initiates oscillations in said chain oscillator,said blocking oscillator including an energy storage device which whencharged maintains said blocking oscillator in its blocked condition,means bleeding the charge from said device and means recharging saiddevice from the output of a succeeding element of said chain oscillator.

References Cited in the file of this patent UNITED STATES PATENTS1,848,839 Ranger Mar. 8, 1932 2,418,116 Grieg Apr. 1, 1947 2,419,292Shepard Apr. 22, 1947

